1. Field of the Invention
This invention relates to an exhaust system control apparatus in an internal combustion engine, primarily for a vehicle such as a motorized two-wheeled vehicle or the like, which has an exhaust passage extending from an engine main body with a subsidiary chamber which is in communication therewith through a communication passage. The communication passage is provided with an opening and closing valve, wherein the opening and closing valve is arranged to be opened and closed according to a set engine speed.
2. Description of the Prior Art
Prior art engines of this type such as a two-cycle engine or the like have been improved by using the positive pressure of a pulsation wave of a combustion gas reflected from an open end portion of an exhaust pipe in the final stage of an exhaust stroke in a high speed operation. The pulsation wave acts on an exhaust port portion and thereby a mixture gas which has been discharged from a cylinder into the exhaust pipe, by pushing it back to the interior of the cylinder. The engine speed at which the output of the engine can be improved is limited to the high speed range where the exhaust pipe is designed in shape or/and size to comply with a high speed range. Consequently there is a lowering in the output at a low speed operation as a result of the negative pressure of the pulsation wave acting on the exhaust port portion causing the mixture gas in the cylinder to be sucked out.
Accordingly, it has been proposed to provide the exhaust passage with a subsidiary chamber which is in communication therewith through a communication passage. The communication passage is provided with an opening and closing valve which is arranged to be opened at a low speed operation and to be closed at a high speed operation. Thus negative pressure at the exhaust port portion caused by the pulsation wave of the combustion gas in the final stage of the exhaust stroke, that otherwise would be the cause of the lowered output, is changed into a positive pressure by a reflection wave from the subsidiary chamber. Thereby the output of the engine is improved, and at a high speed operation of the subsidiary chamber has no influence and thereby the lowered output is prevented. In this arrangement, such as shown in Japanese Utility Model Application Publication No. 132321/1980, an electric motor is usually used for opening and closing the valve, the electric motor being arranged to be operated by an engine speed detector signal. As a result the changeover operation time for opening or closing of the valve becomes long, and also when engine speed is rapidly changed as in the case of a vehicle engine, the opening or closing of the valve corresponding to the engine speed cannot be effected. Accordingly, excellent output characteristics over the whole range from low speed to high speed cannot be obtained. Additionally, there is the inconveniences of providing electric switches for detecting the position of the opening and closing valve and for stopping the valve; and further, electric power consumption is large.